93 | Fiber Fundamentals: Soluble vs Insoluble and the Gut Microbiome

0:00 Hi there. Welcome to In the Clinic with Camille. My name is Camille Freeman. I'm an herbalist and nutritionist. And in this podcast, I share little tips and tidbits that might be helpful for other practitioners. So earlier this week, I taught a class about the gut-brain-nervous system connection and non-nutritive sweeteners. And we had a lot of questions towards the end of the class. And I realized after the question and answer session ended that a couple of people had put in the chat some questions about fiber and what types of fiber specifically are supportive of the gut microbiome. So I thought I would answer that question here for folks who maybe didn't get to come to the class but are still interested in this topic and just to supplement the class itself.

0:43 So let's just talk about fiber very briefly. Now, this is just a very short synopsis. This is a nuanced topic. I could probably do a whole class for an hour and a half on fiber, and maybe I will sometime. I don't know if you're interested. Let me know. But for right now, I just want to go over some bird's eye view, big picture things. All right, so what is dietary fiber? Dietary fiber is carbohydrates and lignans, but mostly carbohydrates that do not get digested in the stomach and small intestine and that make their way into the colon. These typically come from plants, And as you probably know, carbohydrates are just long chains of individual sugar molecules stuck together.

1:23 Okay, so the recommendation for adult humans is that we get, depending on who you're asking, somewhere in the 20 to 35 or more grams per day. Most Americans are getting substantially less than that. I believe the average is something in the 12 to 15 grams per day range, and a lot of people are getting much less than that. One of the things that muddies the waters a little bit when it comes to fiber is soluble versus insoluble. And this is a little unfortunate because it's based on the chemistry of the fibers, but I think it just confuses people when they're thinking about fiber, and it makes it a little bit more complex than it has to be.

2:04 So soluble fiber is fiber that dissolves in water. This means it has a viscous feel to it, generally speaking. This includes things like pectins and gums you're going to find this type of fiber in oats beans apples citrus fruits a lot of things like that and the reason that they dissolve in the water is that they have these they're these long chains of carbohydrates but instead of being one big straight chain it's a bunch of branching chains off of sort of a central one and they have groups on the end that are hydrophilic meaning they're water loving so they form kind of a slime a little bit. All right, so that's soluble. And you can think about it. They're soluble, they dissolve in water. Insoluble fibers are not water soluble. They add bulk, they speed to transit.

2:50 This is things like cellulose and lignin. And the reason that they add bulk is because they don't dissolve in water, but they absorb water. So when the fiber moves through your digestive tract, it's pulling water towards it, and it's bulking up the stool. Now, this is great. Both of these are great things. We'll talk about why in a moment. And most plants or plant foods, plant-based foods, have a mix of both soluble and insoluble. So you'll hear like, oh, apples are rich in pectin, which is soluble. Yes, it is. That is true. But they also have some insoluble fiber. So we can't really categorize foods as soluble or insoluble because, like many things, they are complex.

3:31 They have a bunch of constituents. And generally speaking, most of our plant foods have some soluble, some insoluble, maybe just more or less of one or the other. Okay, so in the colon, the soluble fiber, the type that is viscous and dissolves in the water, is fermentable. What that means is we can't digest it ourselves in terms of the stomach, the small intestine, it's not getting absorbed, and so forth. But when it gets down into the colon, where most of our gut flora live, they can eat this type of fiber. That's what we mean when we say fermentable. That means these gut flora are, quote, digesting this fiber, and that's the process of fermentation.

4:14 And when they do that, they produce gases and they produce short-chain fatty acids. So when they eat the soluble fiber, they make gas, they make short-chain fatty acids. The short-chain fatty acids are quite good for health. The gas can be a little bit problematic depending on your tolerance. We'll talk about that in a second. Insoluble fiber, the bacteria that live in our gut and the other flora that live in the gut, they don't generally have the enzymes that break down the insoluble fiber. So they mostly pass through the colon unchanged. However, they do have this benefit of providing bulk. So really helpful for constipation and that sort of thing, right? Hopefully that makes sense.

4:57 So they both have benefits. The soluble fiber are acting as prebiotics. They're feeding the gut flora. The insoluble fiber is bulking up the stool, making it easier to pass, preventing or treating constipation, and so forth. All right, so our soluble fiber has the benefits of doing things like lowering cholesterol, stabilizing blood sugar, supporting the healthy bacteria and other flora that live in the gut and suppressing the potentially pathogenic bacteria that. Normalizing immune function, regulating the gut-brain-nervous system axis, and so forth. And it does all of that via increasing the amount of short-chain fatty acids.

5:38 So you need the soluble fiber that gets, quote, digested or fermented by the gut flora and produces short-chain fatty acids, which then have systemic effects that are helpful. They also have local effects that are helpful within the digestive tract themselves. Okay? So how do we get fiber? How do we advise clients about getting fiber and that sort of thing? Well, first of all, the main thing is just getting plenty of whole plant foods. So this would be things like whole grains, nuts, fruits and veggies, that sort of thing. It's pretty easy to look at what somebody's eating for a few days and get a feel for if they are in the appropriate range of fiber intake or not, but it can be helpful to track for a few days.

6:19 If not, I'm really looking for something in the range of 25 to 30 or more grams of fiber overall per day. If somebody is not able to get that amount of fiber in their diet, or for whatever reason, a supplement seems like it might be a better choice, a lot of times psyllium is my go-to. And the reason that psyllium, I find, is a really optimal choice is because it has a mix of soluble and insoluble fiber. So it's mostly soluble. And remember, the soluble form of fiber is what is feeding the healthy gut flora. Okay, so I really like psyllium as a first choice for people.

7:00 If somebody is primarily struggling with constipation, then sometimes you'll see supplements like wheat bran or cellulose, etc., that are more insoluble. However, I find that even when somebody is having constipation, the psyllium is going to provide some insoluble fibers and some bulking. So I find that it's a nice, happy medium for both. Now, you have probably heard about other types of prebiotics, such as fructooligosaccharides and so forth, inulin, etc. These are also constituents of plants, and they are technically considered fiber.

7:42 An oligosaccharide is basically a smaller chain of a bunch of sugars put together. So often we wouldn't think of it as a fiber. However, in terms of the action in the body, they are counted as fibers. So things like FOS, GOS, inulin, these are technically considered fibers. They are not broken down in the small intestine. We don't. Individually as humans digest them, but when they get into the colon, our gut flora can digest them. They are fermented just like some of the other fibers we were talking about before. Now, the reason that you aren't usually going to see like a fiber powder that's entirely made of FOS or inulin is because these types of fibers are, because they're shorter and smaller, they are fermented or digested by the gut flora very quickly.

8:31 And they therefore produce a high level of gas, which for a lot of people can be uncomfortable, can cause some bloating, can cause some discomfort, some cramping, and that sort of thing. So these ones, while they are technically fibers and they are prebiotics in that they are feeding the healthy, beneficial gut flora, we generally do better with them in smaller amounts. And of course, we have some people, such as those with IBS and other types of digestive issues, where they may do better of whitting them mostly or entirely. So they're more rapidly fermented, they produce more gas, and so forth. So a few last things I'll say to you about fiber is that if somebody is starting from a low fiber situation, we want to build up really, really slowly.

9:17 We want to start with just a small increase. We don't want to go immediately from 10 grams of fiber a day to 25, because what will happen is that person will have cramping, they'll have diarrhea, they will not be happy with you. So the recommendation that I provide for you as a practitioner is to gradually increase. My standard recommendation is let's add one or two servings of fruits and vegetables per day for a few weeks and then slowly go up from there. And if you need a supplement, same thing, start with a very small dose of the supplement and gradually build up from that point. We're not going to get into full contraindications, but I do like to mention that there are certain situations where fiber supplementation is not possible or not optimal, and perhaps we'll get into that in another podcast episode.

10:08 But for right now, let's just say that these recommendations are for the general population who do not have any major digestive-related conditions. And if somebody does have something like diverticulitis, diverticulosis, any kind of surgery, Crohn's disease, etc., you may need to think more carefully. You want to have specialized training, make sure that you know what you're doing. This is just for the average person without any serious GI-related symptoms. Diagnoses. Okay, so I hope that helps clear up the differences between soluble and insoluble fiber and how they may or may not affect the gut flora. Just as a recap, soluble fiber serves as food for our healthy, beneficial gut flora.

10:56 Insoluble fiber does not seem to directly impact the gut flora, but it does impact digestion by bulking up the stool, making it easier to pass, and therefore it probably has indirect effects on the gut flora. Okay, I hope that's clear. If you have any questions, let me know. And lastly, if you're interested in all this, the ins and outs of supplementation and things like that, next year in 2026, I am doing a supplement deep dive. This is one continuing education class per month for practitioners. You can sign up and get on the wait list if you go to camillefreeman.com slash supplement soon.

11:37 And you can see all the different topics that we're going to be covering. You can get on the wait list, which also includes a special discount when the course opens in January. I'd love to have you there. We're going to do some really interesting topics and just learn more about how to advise clients about some of the different supplements that are on the market, including fad supplements, as well as some of the more standard ones that many clients are taking, but maybe not in appropriate doses, in appropriate forms, and maybe not for the appropriate reasons. So we're going to talk about all of that next year. I'd love for you to join us. If you have questions, please reach out to me anytime. I'd love to hear from you. Otherwise, I hope you have a lovely rest of your day.